This invention relates to a method and apparatus for recording data transmitted from, e.g., a computer on an azimuth track of a magnetic tape by a rotary head.
In a computer, it is frequently practiced to transfer data recorded on, e.g., a hard disc to a data recorder termed a data streamer, e.g., once every day for protecting the data.
Up to now, a conventional analog audio tape recorder has preferentially been used as the above data recorder. However, with the analog audio tape recorder, the amount of consumption of the magnetic tape is increased excessively, while data recording and transfer become time-consuming because of the low data recording rate. In addition, since high-speed retrieval is not feasible with the analog audio tape recorder, searching or locating of a data start portion is also time-consuming.
Thus it has been practiced to use a helical-scan digital audio tape recorder employing a rotary head, or a so-called DAT, as the data recorder.
When employing the DAT as the tape recorder, data from a host computer are converted into data of a DAT format before being recorded. With the DAT format, each frame is constituted by two azimuth tracks T.sub.A, T.sub.B formed during one complete revolution of two heads with different azimuth angles, and 16-bit PCM audio data are recorded by an interleaving technique with one frame as a recording unit, as shown in FIG. 1. Each track is made up of 196 blocks, each block consisting of 36 bytes. Of these blocks, both terminal 34 blocks are sub-areas, with the mid 128 blocks being a main area.
Each sub-area is divided, beginning from one track end, into a merging portion, a preamble portion for sub-code PLL, a first subcode portion, a post-ample portion, a gap portion between adjacent blocks, automatic track finding (tracking) signal portion or ATF portion, a gap portion between adjacent blocks, a preamble portion for data PLL, a pre-amble portion for adjacent blocks, an ATF signal portion, a gap portion between adjacent blocks, a preamble portion for subcode PLL, a second subcode portion, a postamble portion, a gap portion between adjacent blocks and a merging portion. Each of the first and second subcode blocks is made up of 8 blocks, with the remaining portions being made up of respective pre-set number of blocks.
The main area is made up of 128 blocks. Each data block has one byte each of the synchronization signal, PCM.ID, block address and the parity, beginning from its leading end. Main data is arrayed in the next following 32 bytes, as shown in FIG. 2.
If the data is audio signals, the main data is 16-bit PCM data for the left channel and 16-bit PCM data for the right channel. The 16-bit main data are interleaved in the main areas of two tracks constituting a frame and arrayed along with parity Q data, as shown in FIG. 3. In this case, about 5760 bytes of data are recorded in the main area of one frame.
By dividing a track into the main area and the sub-area, post-recording may be made with the DAT format, using the sub-area.
The construction of the error correction code for main data in the DAT format is the product code as shown in FIG. 4, with the code plane being made up of four sub-planes per track. Each sub-plane is coded in C1 and C2 directions.
If the data recorder is employed as a data recorder, data transmitted from a host computer is converted to 16-bit data which is treated in the same way as the PCM data and formatted for recording in a one-frame main area. In this case, 2-byte 16-bit data for the L and R channels are used, of which upper four bits, for example, are recorded as format ID and the remaining eight bits are recorded as a logical frame number. The format ID indicates the format proper to the data recorder. Logical frame numbers of 1 to 23 are affixed to each of 23 frames as a unit.
As a format of a data recorder employing such DAT, the formats DDS and DDS2, for example, are prescribed under the standard of the European Computer Manufacturers Association (ECMA).
With the DDS or DDS2 format, a device region from a physical tape beginning position or physical beginning of tape (PBOT) up to a logical tape beginning position or logical beginning of tape (LBOT) is prescribed in a leading area consecutive to the leader tape as being a region for effecting tape loading and unloading. The device region is followed by a reference region and a system region. The reference region is used as a physical reference for recording a system log (hysteresis information) in the system region. A data region for data recording is recorded next to the system region, and an end-of-data (EOD) region is recorded next to the data region.
The DDS2 format also provides a two-partition tape having two partitions P1 and P2 each having a reference region, a system region, a data region and an EOD region. The system log, that is the hysteresis information, is recorded in the system region of each of the partitions P1 and P2. The system log is recorded by multiplex recording in a sub-code region of the system area in the form of a pack.
With the above-described DDS or DDS2 format, the system log for each partition is individually recorded in each system region of each of the partitions. Thus it becomes necessary to access the system regions when loading/unloading the tape, thereby consuming a lot of time for loading/unloading.
Since the system region is recorded or reproduced a number of times, tape damage become excessive thus necessitating multiplex recording. Since the error correction coding is not provided for the sub-code region, the sub-code region is lower in reliability than the main data.
As for the firmware, accessing of data recorded by multiplex recording for improving reliability consumes a lot of time. In effect, checking can be made only up to the frame time limit. In addition, the sorts of items that can be written are limited, if in the form of the pack.